1. Field of the Invention.
This invention deals with the treatment of respiratory difficulty arising from an inability to at least partially eliminate sputum or secretions from the airway of a mammalian subject. The treatment of such respiratory difficulties typically arises in patients having limited spinal nervous function such as from quadriplegia or multiple sclerosis.
2. Description of the Art Practices.
In a normally functioning mammalian subject the breathing function occurs automatically with a periodic cough reflex when the subject senses the build up sputum or secretions in the airway. The sputum or secretions in the airway are the result from the normal operation of the mucosa in lubricating the airway and in trapping foreign material.
However, if the sputum or secretions are not periodically removed it will impair the subjects ability to obtain air through the airway. Secondly, if the build up of the sputum or secretions in the airway is sufficient it may result in complete blockage of the airway leading to asphyxia of the subject.
In U.S. Pat. No. 3,658,651 issued Apr. 25, 1972 to Maclean there is discussed a method of treatment by placing a patient or an animal to be treated between the poles of an electromagnet. The patient or an animal is then subjected to an a pulsating magnetic field induced by an intermittent direct current to the electromagnet with the peak intensity of each pulse being at least 2,000 gauss. The Maclean patent discusses as potential effects of his treatment the clearing of the stimulation of the endocrine glands, relief of pain, suppression of cough, and pleural effusion, energizing effects, clearing of the sensorium, relaxation of muscle spasm, development of peace of mind, and sense of well being, and increase of libido.
Linder in U.S. Pat. No. 5,190,036 issued Mar. 2, 1993 teaches an abdominal binder comprising an electrode belt for stimulating cough in a quadriplegic patient. Linder further discusses stimulating cough in a quadriplegic patient Chest Volume 103 number 1 January 1993 pages 166-199 article entitled Functional Electrical Stimulation to Enhance Cough in Quadriplegia.
Mouchawar, in an article entitled Closed-Chest Cardiac Stimulation with a Pulsed Magnetic Field, Medical & Biological Engineering & Computing March 1992, page 162 discusses magnetic stimulator to generate intense, rapidly changing magnetic fields capable of stimulating nerves. Magnetic resonance systems utilizing coplanar coils to provide a pulsed magnetic field with an average of 12 kilojoules to achieve closed-chest magnetically induced ectopic beats. The Mouchawar article also describes the peak-induced electrical field for threshold stimulation at 213 V/m for a 571 micro-second damped sine wave pulse.
Mouchawar et al., in an article entitled Magnetic Electro-phrenic Nerve Stimulation to Produce Inspiration, published in the Annals of Biomedical Engineering, Volume 19, 1991 pages 219-221 discusses producing inspiration in a dog. The induced inspiration reported by Mouchawar et al. is plotted by integrating the inspiratory air-flow velocity record.
The author of the present patent published a note in entitled Magnetic Stimulation of the Intercostal Muscles at page 1237 of the Archives of Physical Medicine and Rehabilitation volume 74, November 1993. The present author has contributed to a note entitled the High Frequency Magnetic Stimulation of the Inspiratory Muscles which was published in Muscle & Nerve October 1993 Volume 16 number 10 at page 1088.
Manual methods of aiding respiration are discussed in U.S. Pat. No. 4,977,889 issued Dec. 18, 1990 to Budd. In the Budd patent a vest is utilized to stimulate respiration.
In a paper entitled Thoracic Spinal Nerve and Root Conduction: A Magnetic Stimulation Study Magnetic Stimulation of the Thoracic Nerves is discussed by Chokroverty et al. The Chokroverty et al. article was published in Muscle & Nerve September 1995 Volume 18, number 10 at pages 987-991.
Percutaneous magnetic stimulation is discussed in an article entitled Ventilatory Effects of Percutaneous Magnetophrenic Stimulation by Nagano et al. The Nagano et al. article was published in the Frontiers of Medical Biological Engineering, Volume 3, Number 2, pages 97-112 in 1991. An article entitled Cough in Spinal Cord Injured Patients: Comparison of Three Methods to Produce Cough was published by Jaeger et al. in the Archives of Physical Medical Rehabilitation Volume 74, December 1993 at pages 1358-1361. The Jaeger article, discusses various methods of phrenic nerve stimulation. Jaeger discloses artificial cough reflex stimulation in U.S. Pat. No. 5,314,454 issued May 24, 1994.
The effect of lung volume on transdiaphrematic pressure is discussed in an article by Hamnegard et al. The Hamnegard et al. article appears in the European Respiratory Journal 1995 Volume 8, pages 1532-1536.
Voorhees III et al., in a technical note in the Journal of Clinical Engineering September/October 1990 page 407 entitled Magnetically Induced Contraction of the Inspiratory Muscles in Dog discusses short-duration inspirations by discharging a capacitor bank into an excitation coil placed over the lower right chest. The Voorhees III article discusses utilizing the construction of the excitation coil as having 59 turns of 1/4 inch copper ribbon 0.0200 inches thick wound on a 3/4" diameter plastic rod where the outer diameter of the coil is 3.75" and the entire coil is potted in silicon rubber.
The inductance per Voorhees III et al. is 139 micro-H and the resistance is 0.084 ohms. The current was delivered to the coil from a 100-micro F capacitor bank. The resonant frequency of the system was 1350 Hz and the damping coefficient was 0.05.
Cadwell Laboratories, Inc. in Application Notes AP-2 Rev. 1 Feb. 22, 1990, discusses high speed magnetic stimulator characteristics.
In an article entitled Developing a More Focal Magnetic Stimulator Part I: Some Basic Principals by Cohen et al., as recorded in Journal of Clinical Neurophysiology, 8 (1); 102-111 (1991) magnetic stimulation is discussed generally. Similar disclosures are made by Yunokuchi et al. in the Journal of Clinical Neurophysiology, 8 (1); 112-120 (1991) in an article entitled Developing a More Focal Magnetic Stimulator. Part II: Fabricating Coils and Measuring Induced Current Distributions.
The reader is also referred to Magnetic Stimulation in Clinical Neurophysiology edited by Sudhansu Chokroverty and published by Butterworths, Boston, London, Singapore, Sydney, Toronto, and Wellington Chapter 3 pages 17 through 32, pages showing FIGS. 7-18; 14-1; 17-4; 17-10, 18-3 and 18-4.
Further reference is made to Magnetic Brain Stimulation With a Double Coil: The importance of Coil Orientation by Mills et al. published in Electroencephalography and Clinical Neurophysiology, 85 (1992) pages 17-21. Reference is also made to a publication entitled the Effects of Coil Design on Delivery of Focal Magnetic Stimulation-Technical Considerations Cohen et al., in Electroencephalography and Clinical Neurophysiology, 75 (1990) pages 350-357.
The assessment of nerve and muscle function is discussed in a paper entitled Comparison of Cervical Magnetic Stimulation and Bilateral Percutaneous Electrical Stimulation of the Phrenic Nerves in Normal Subjects as reported in European Respiratory Journal 1994 Volume 7, pages 1788-1702
A summary of the results presented in this patent was submitted for publication entitled Functional Magnetic Stimulation of The Expiratory Muscles for Cough by Lin et al.
To the extent that the foregoing references are relevant to the present invention, they are herein specifically incorporated by reference. Where temperatures are given, they are in degrees C unless otherwise indicated. Pressure measurements are reported in centimeters of water. Percentages and ratios given herein are by weight unless otherwise indicated. Measurements herein are stated in degrees of approximation and where appropriate the word "about" may be inserted before any measurement.